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Weegy: Since you're not going for longest lasting or cheapest only, you want to work out the most efficient Ah / R rating (Amp/hour per Rand)
Since battery load has a non-linear discharge curve, [ you can't just grind it for 2hrs to see which gave you the most amount amps before it poked either.
Ah = how much amps a battery can supply at a constant rate for an hour ... usually you measure it in a 20hr run. So a 20Ah battery, will provide 1amp constant for a period of 20hrs before it's done. (20Ah = 20hrs x 1amp)
So what you want to do is attach a load to the circuit that will draw X amount of amps constant. Then you measure how long it runs for (e.g. your clock experiment) This will let you know which battery was able to supply the required load for the longest.
Once you have that figure, work out how expensive the battery was in comparison to its rivals. If it is twice as expensive, it has to last at least twice as long (have 2x the Ah rating) in order to be the most cost effective one. But then also for bonus marks, look at the complete system, and not just the controlled experiment - space costs money. It's more expensive to house 2 batteries than to house just one, since it costs more material and packaging / transport.
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